Portable greenhouse



FIG. 1 is a top, front perspective view of a portable greenhouse, showing the new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is a right side elevation view thereof, the left side being substantially a mirror image thereof, the only difference being the position of the legs at the front of the design;

FIG. 5 is a bottom plan view thereof; and,

FIG. 6 is a rear elevation view thereof.

The broken lines depict environmental subject matter only and form no part of the claimed design. 

The ornamental design for a portable greenhouse, as shown and described. 